WHEN it comes to fighting the potentially deadly West Nile virus, New York is between a rock and a hard place.

Environmental groups say the city is spraying too many toxic pesticides, over too wide an area, for too little effect.

The mayor and the city’s health officials counter that they’re following federal guidelines – they’re spraying at appropriate times, using the proper dosage and the spray products they use are safe.

But as the threat from virus-carrying insects looms over the city, experts who fight mosquitoes across the United States say that both sides are right.

“Consider the fact that in New York, they’re looking at a new virus in a new land,” said Jonathan Day, an entomologist at the University of Florida in Vero Beach. Day has studied St. Louis Encephalitis, also spread by insects, and is now involved in monitoring the West Nile virus in New York.

“Last year, they were criticized [that they did spraying] too late, and this year, they’re criticized for being too early.

“Until this virus becomes more established and more predictable, then perhaps what they’re doing is warranted.”

Day empathizes with city officials.

“You almost have to go overboard the first year of surveillance because there is no baseline,” he said.

“We’ve got about a 25-year baseline” with St. Louis Encephalitis in Florida, Day added. “As soon as those [sentinel] chickens start to show up positive [for the virus], we know what our reaction should be.”

Florida authorities have devised a careful step-by-step procedure for when a medical emergency is indicated – when a chicken, bird or mosquito shows up infected.

First there is a medical advisory, then a medical alert, and finally, spraying.

“In this county, about 40 percent of our sentinel chickens [showing they’ve been infected] triggers spraying,” Day said.

This year so far, none of the sentinel chickens located at 14 monitoring spots around the city have tested positive for the virus. Thirty-three wild birds have died of the disease, most on Staten Island, and several mosquito trappings around the city have turned up bugs infected with West Nile.

IN 1999, the debut year for the West Nile virus in this hemisphere, seven people died and 62 got sick.

This year, there’s been three human cases reported. A 78-year-old man from Staten Island was the first reported illness, and he is now recovering. Yesterday, officials reported also a 63-year-old man and a 64-year-old woman, both from Staten Island, also had been hospitalized with the disease, and are now at home recovering.

“The city says there may be a few people who might be more strongly affected [by the virus] but that most people won’t know [if they have it],” said Cathryn Swan of the New York Environmental Law Project and No Spray Coalition.

“From our perspective, if that’s the case, then spraying isn’t necessarily the way to go.”

Environmentalists add the city has overreacted.

“We are spraying millions of people with a toxic chemical,” said John Bianchi of the National Audubon Society. “We are not erring on the side of caution.”

There are several methods of controlling mosquitoes, and New York has adopted two main strategies.

A first attack wave is to larvacide where mosquitoes breed – killing the bugs while they are still in the larva stage.

A second assault tactic is to target the adult mosquito with pesticide spray, either from the ground or the air.

Health Department spokeswoman Sandra Mullin said the city believes “we’re applying pesticides in a limited and prudent fashion, and only in those instances where we identify viral activity. Our principal control measures continue to be larvacide application, and urging the public to take personal precaution.”

In addition to its larvacide assault, the city has carried out extensive ground spraying in some areas of every borough – including Central Park in Manhattan and all of Staten Island.

But environmentalists actually question the effectiveness of a spraying program. They charge that ground spraying hits only about 1 percent of adult mosquitoes.

RAY PARSONS, the head of the Harris County Mosquito Control Program in Houston, Texas, disputes the environmentalists’ charge – although he’s got little enough statistical ammunition of his own with which to argue.

“Right now, we can’t evaluate the effect of a spraying,” he said. “There’s got to be a lot more research.”

Parsons guesses spraying hits about 30 percent of the adult bugs at a time – but it’s a figure based on caged bugs, not bugs in the wild.

“No one knows,” he said. “We’re making a scientific guess. It depends on the neighborhood and the habitat you’re spraying on.”

And that means spraying houses in a Houston suburb may be completely different than spraying a New York City neighborhood.

“If you can control mosquitoes without pesticides you’re better off,” Parsons added. “But when you have an outbreak, you have to spray by truck. That’s life.”

As to the safety of the pesticides being used in New York neighborhoods, one expert points out that most public health officials have to rely on the Environmental Protection Agency and its research of products.

“The states don’t really have the resources for all the evaluation these products need,” said Linn Haramis, an entomologist for the Department of Public Health in Illinois.

“You’re never going to find a totally non-toxic pesticide, or it wouldn’t work.”

Haramis said aerial spraying is “the most effective way [of controlling] adult mosquitoes,” but added that larvaciding “should be primary.”

“In a public-health situation, where people can potentially die, it’s pretty serious,” he added. “I don’t think public health officials [in New York City] had a whole lot of choice.”